The invention relates to a antenna system for a mobile unit that allows the gain characteristics of an antenna array to be matched to the geographic location of the mobile unit, and more particularly to an antenna system which allows a mobile unit user to enter geographic information which is used for the adjustment of the antenna array gain characteristics.
Communications systems such as satellite-to-mobile unit communications systems require a mobile unit receiver antenna that performs well along the expected satellite elevation angle range. FIG. 1 depicts a communications system 10 comprising a satellite 12 and a mobile unit 14 for illustrative purposes. If the satellite is in a geosynchronous orbit, the elevation angle changes (e.g., between 60 degrees and 21 degrees) depending on the geographic area in which the mobile unit 14 is located. If the satellite 12 operates in an elliptical orbit, as opposed to a geosynchronous orbit, the elevation angle changes in accordance with time, as well as with the geographic location of the mobile unit 14. A need exists for an antenna system which maximizes signal reception in accordance with changes in the satellite elevation angle.
An electronically steerable antenna is described in U.S. Pat. No. 5,349,360 which changes antenna operation mode (e.g., diversity mode or multiplex wave suppressing adaptive array mode), depending on whether the antenna is in an urban area or a suburban area The antenna is mounted in a vehicle. A navigation system such as a Global Positioning System (GPS) receiver or the like is used to determine the current vehicle position. Stored file structures allow for selection of one of the operating modes based on the GPS position information to adjust the antenna elements in an antenna array.
The steerable antenna described in the U.S. Pat. No. 5,349,360, however, does not adjust antenna elements to accommodate changes in satellite elevation angle and therefore maximize signal reception. Further, the steerable antenna does not adjust antenna elements in accordance with mobile unit location data provided by a user. An advantage to using location data provided by the user is the possibility of eliminating the GPS receiver to reduce the complexity and cost of a satellite-to-mobile unit communications receiver.
In accordance with the present invention, an antenna system is provided for use in a mobile unit in a satellite-to-mobile unit communications system which comprises an antenna array and an antenna array control module for controlling the gain characteristics of the antenna array in accordance with the geographic location of the mobile unit and the corresponding elevation angle between the mobile unit and the satellite.
In accordance with an aspect of the present invention, the antenna system is controlled in accordance with array patterns for maximizing signal reception when the elevation angle is either a low elevation angle or a high elevation angle.
In accordance with yet another aspect of the present invention, an array pattern for the antenna array is selected based on the geographic location of the mobile unit as provided by a user. The satellite receiver unit can be provided with user input control devices.
In accordance with still yet another aspect of the present invention, the antenna array is controlled using antenna element control data which is stored in tables that specify an antenna pattern for optimizing reception at high and low elevation angles and which is selected based on mobile unit location data.